Nowadays, Lithium (Li) is considered a strategic metal whose use has been significantly expanded. Among other applications, Li and its compounds are used in the manufacturing of lubricants, in the manufacturing of glass and special alloys. Moreover, it forms part of medicament formulation for psychiatric medication. The current high demand constitutes its use as a component of the Li ion and Lithium-polymer type batteries, used in calculators, video recorders, laptop computers, cell phones and other electronic equipment, as well as in weapons and automatic probe equipment. In the case of larger batteries, its use is extended to communications equipment as well as the automotive industry. A potentially important use of lithium is atomic fusion, wherein by means of bombardment with neutrons, isotope 6 of lithium is transformed in tritium which in turn, is fused with deuterium to form helium, both reactions producing a great amount of energy. In this context, it is essential to develop new techniques which allow for its extraction from primary sources poorly exploited.
Lithium is a relatively rare metal in nature, however, it is found in many minerals due to its high chemical reactivity. Nevertheless, a few minerals exist which are commercially useful for the production of lithium, being spodumene the most important, which generally is found mixed with quartz, feldspar and mica, with a maximum theoretical Li2O content of 8.03%.
In Argentina, the main lithium deposits are divided into those from salt lakes and those of spodumene. The salt lake with the highest lithium content is located between the provinces of Salta and Catamarca, and is known as “El Salar del Hombre Muerto”, with an amount of 800,000 tons of lithium. The main reservoirs of spodumene are located in the provinces of Salta, San Luis and Córdoba, and are characterized by having a large mineralogical variability.
Spodumene has the formula LiAlSi2O6. At temperatures higher than 1000° C. natural phase α-spodumene undergoes an irreversible change to phase β-spodumene, this phase change requires an important energy load which increases the process cost.
The most widely used methodologies for the extraction of lithium from spodumene at an industrial level may be divided into:
A) acid digestion, by lixiviating the β-spodumene mineral with concentrated sulfuric acid at a temperature above 250° C. The obtained lithium sulfate is converted into lithium carbonate by adding calcium carbonate to the pulp, this being the final product of the process;
B) alkaline digestion, where α-spodumene is treated with CaO at 1040° C., to obtain lithium oxide, which is then hydrolyzed to obtain lithium hydroxide as a final product;
C) ion exchange, where β-spodumene is heated with sodium or potassium carbonates at 400° C., to produce an exchange of the cation of the carbonate for Li+. The final product obtained is lithium carbonate.
In the state of the art several processes have been disclosed, for example, dissolution of β-spodumene in autoclave at temperatures above 250° C. Other authors suggest the combination of pyro- and hydrometallurgical processes, first carrying out the calcination of β-spodumene with some Na or Ca salt (Cl−, SO4−2, CO3−2) and then, dissolution in water of the mixture obtained.
Lepidolite has a theoretical content of Li2O of 4%, together with petalite, they are mainly used as minerals in glass and ceramic industry.
The most widely used methodologies for the extraction of lithium from lepidolite or petalite at an industrial level are, similarly to spodumene: acid or alkaline digestion and ion exchange, similar to those used for the processing of spodumene, previously described.
Petalite has a theoretical content of LizO of 4.9%, has the formula LiAlSi4O10. At temperatures above 1100° C. it undergoes an irreversible change to phase β-spodumene and SiO2, this phase change requires a great energy load and hence increases the costs of the process.